I’m back once again with even more information from Lightroom developer Eric Chan, and best practices for creating HDR RAW files in Lightroom CC 2015 / 6. Previously we reported that Adobe recommends just two exposures for creating an HDR DNG file, which was and is true, but now Eric expands on that idea, and explains under what conditions you might want to add more than two exposures. Before we begin, if you haven’t caught up on this topic, check out Part 1 or Part 2 in this series.
Eric starts with some advice on merge speed:
More images in an HDR merge will take proportionally longer. 2 frames is [normal,] 3 frames is even longer, etc.
Whether or not a third (middle) frame will help will depend on a lot of things, including the tonal content of your scene, and the spread of your exposure bracket. Keep in mind that a third frame increases the likelihood of misalignment between the frames.
If merging two frames, I generally recommend they be within 3 stops of each other. For example, I’ll capture one shot for the highlights, then open up 3 stops and capture another frame, then blend those two.
I don’t recommend merging two frames that are super-spread apart. Continuing the above example, I would NOT recommend shooting my second image by opening up 6 stops. Why not? Because I am likely to see some range of tones in the merged result that are visibly more noisy than other tones. These are the pixels that are clipped in the 2nd (bright) shot, and therefore the HDR blending algorithm needs to grab those tones from the 1st (dark) shot, which is noisier for those pixels.
So it’s fine to use the in-camera HDR bracket facilities, including ones that allow you to take 3 shots quickly, like 0/+3/-3.
0/+1/-1: I would just merge the +1 and -1 shots (they’re within 2 stops of each).
0/+2/-2: I would merge either the 0/+2 shots or 0/-2 shots (depends on how I metered the scene). For very high contrast scenes, I’d merge all three.
0/+3/-3: Similar to the 0/+2/-2 case.
I would consider the +1,5/-1,5 case “3 stops apart”.
The +3/-3 case would be 6 stops apart.
So there you have a more detailed version of “best practices” for shooting Lightroom HDR.
If you’re a Canon 5d mk III user, you likely know that you have an in-camera HDR function. The camera produces a merged JPEG for you, but it also keeps the RAW files. You can use this and just ignore the JPEG. I do not own a 6D or a 7D mk II, but since they’re also newer Canon bodies, I suspect they may have the HDR feature as well.
If you don’t have one of these bodies, or if you want more control over the bracketing, or if you’re on the 1DX, you can also use the AEB tools to create 2, 3, 5, or 7 shots bracketed at any difference from 1/3 to 3 stops each. Check out the AEB section of your manual, or do a little Googling to learn how to use these features.
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